Composite materials that consist of a fibrous material and a matrix (often polymeric) material have found widespread use in wind turbine blades, naval structures and ship hulls, aircraft structure, sporting equipment and others.
The strength and quality of such structures and products depends strongly on the fibres and/or yarns to be straight.
Any disruption, wrinkling, bulges and waviness created when handling the fibres and/or yarns may thus be highly undesirable as they will weaken the finished structure. However, as these fibres and/or yarns in their virgin state are very flexible and difficult to handle, there is a considerable risk of creating said defects when placing and handling the fibres during manufacturing of previously mentioned components. The risk is especially high, when attempting to handle stacks of multiple fibres, yarns or fabrics.
One way of making the handling of fibres and yarns easier is by stitching them together, thus creating a fabric. The number of fibres that constitute a fabric can be varied to suit the requirements of the structure, e.g. a fabric with many fibres can be used in one place and a fabric with fewer fibres can be used in another place. This thus requires the manufacturing of at least two different fabrics. This can increase costs, as approximately 50% of cost of a fabric is the cost of arranging the fibres into a fabric.
An alternative way of achieving areas with varying amounts of fibres is to use a fabric with relatively few fibres, and then stack a number of fabrics on top of each other to achieve the desired number of fibres in that area and to make a gradual transition between areas with different requirements to the number of fibres. The main disadvantage of this solution is that any overlapping or stacked fabrics must be placed in sequence, which is a disadvantage for production time in an industrial application.
Another disadvantage with using fabrics is that a bulge or wrinkle may not be isolated to a single fibre, but rather affects the entire fabric thus increasing the extents of the defect